1. Field of the Invention
This specification relates to radio communication, and more particularly, to a method and apparatus for communication between a base station and a user equipment (UE) in a radio communication system which supports carrier aggregation (CA).
2. Related Art
One of requirements of a radio communication system is to support a high data transmission rate. To this end, various technologies such as a multiple input multiple output (MIMO), a cooperative multiple point transmission (COMP), a relay, and a carrier aggregation are being studied.
The carrier aggregation is a concept which bonds a plurality of bands as one system. In this case, each independently operable band may be called a component carrier (CC).
Further, the UE and the base station may perform communication by using various kinds of carriers (or cells). In the case of a general carrier which is used in a 3GPP LTE system, a cell specific reference signal (CRS) is used through all subframes, and a synchronization signal (SS) is included in some of the subframes. Further, a physical downlink control channel (PDCCH) is included in each subframe.